1. Field of the Invention
Pressure responsive distributing valves.
2. Prior Art
Conventionally, accumulator charging valves are used in systems where a first and second user component are employed. Conventionally the second user component, for example a vehicular hydraulic brake system, is provided with a pressure accumulator. Normally, the first user component is a hydraulic power steering system for an automotive vehicle. When the conventional system uses an accumulator for supplying the brake system as part of a second user component and a power steering unit as the first unit component, reasons of safety require that the second user component have priority over the first user component with regard to the supply of pressure fluid.
From German unexamined and printed application DT-OS No. 2,364,413, it is known to provide an accumulator charging valve for distributing the fluid under pressure delivered by a fluid pressure source to two user components connecting with an accumulator. Leading from the fluid pressure source, a fluid line leads through a check valve to the user port which connects with the accumulator. Another fluid line leads through a pilot valve which changes its position in response to the accumulator pressure present in a control chamber of a control valve which permits control of the cross-sectional area of the passage through the line connecting the fluid source with another user component. The control valve comprises a control piston, one end of which projects into the control chamber and the other end thereof is directed towards the line leading from the fluid pressure source. The cross-section of the area of the passage of a line branching off from this connecting line and leading to a user component can be adjusted by the control piston. A pressure spring which is disposed in the control chamber acts on the control piston in the direction so as to close the control valve.
In the known system the accumulator pressure responsive pilot valve changes its position when the pressure in the accumulator reaches and exceeds a predetermined pressure thereby shutting off the line connecting the fluid source to the control chamber. At the same time the pilot valve opens a line between the control chamber and a return line so that the control piston, upon which the pressure from the fluid source was acting, is relieved. In order that a pressure differential be generated on either side of the control piston of the pilot valve when the control chamber communicates with the fluid pressure source, a throttle is disposed in the line connecting the fluid pressure source with the control chamber. In the known accumulator charging valve, which first supplies the accumulator, even when the accumulator reaches a predetermined charging pressure, has the disadvantage that with the accumulator fully charged and the fluid flow from the pressure source switching over to the user component supplied through the control valve, the pressure increase occurring at the user port and exceeding the pressure level of the pressure source and the accumulator causes the fluid under high pressure to act on the accumulator. This has resulted in damage to the accumulator which is only adapted to receive a pressure corresponding to the switching pressure of the pilot valve.
One of the desired goals of the pressure-responsive valve is to overcome the disadvantage of the system above described as illustrated in German unexamined and printed application DT-OS No. 2,364,413, by preventing the pressure from exceeding a predetermined level at the second user component when the pressure at the first user component exceeds the predetermined pressure level and which, at the same time, supplies the second user component prior to the first user component when the pressure by the second user component falls below a predetermined level. This result is known from German examined and printed application DT-AS No. 2,003,554 which illustrates a regulating valve which communicates with a pump and feeds fluid under pressure to a first and second user component. An accumulator is disposed in the line connecting the regulating valve to the second user component. The connecting line from the pump terminates in a chamber of a control valve with lines leading off from the chamber to the first and second user components. Displaceably arranged in the chamber is a piston with the pressure from the pump being applied to one fluid end. The opposite fluid end of the piston is acted on by a pressure spring supporting itself against the bottom of the chamber which rests against the piston. In addition, a reduced pressure, as compared to the pressure of the fluid from the pump, acts on the fluid end, which pressure results from a connection of both piston fluid ends through a throttle in the piston.
In the system of German examined and printed publication DT-AS No. 2,003,554, the lines connecting with the first and second components terminate in the chamber of the control valve in such a way that, in the end position of the piston in the direction towards where the line which comes from the pump terminates, in the chamber, the line connected with the first user component is closed and the line in communication with the second user component is connected to the reduced pressure area of the chamber. When the piston is displaced against the reduced pressure and the pressure exerted by the spring, a connection will be established between the first user component and the area of the control valve chamber which is subjected to the pressure of the fluid from the pump. At this point the connecting line between the reduced area control valve chamber and the second user component will be shut off. At the same time a piston closes a further line leading from the reduced pressure area to a return line through a pilot valve. The pilot valve changes its position in response to the pressure prevailing at the second user component thus opening its passage to the flow of fluid when the second user component has reached a predetermined switching pressure thereby connecting the reduced pressure area of the control valve chamber with the return line and relieving it from pressure. This produces a result in which the displacement of the piston in its end position into the reduced pressure area of the control valve chamber closes the line connecting with the second user component and opens the line connecting with the first user component. By that device the pressure at the first user component, which is higher than the switching pressure of the pilot valve, is not capable of acting on the second user component and consequently on the accumulator. Thus the regulating valve described in German examined and printed Application DT-AS No. 2,003,554 fails to accomplish the desired results.